In this project, the effects of diet upon lens development and viability are studied with specific emphasis on the nutrients tryptophan, vitamin E, and selenium. A nutritional deficit in tryptophan is cataractogenic during either prenatal or postnatal life. Small nuclear opacities occur in 30-90% of lenses from rats at weaning when maternal diets contained 45% the required tryptophan and no vitamin E. Rat pups have normal weight at birth, but are only 50% normal weight at weaning. This abnormal lens appears to result from developmental perturbation since we have been unable to find persistent biochemical changes in lens Na, K, H2O, total protein, and specific lens crystallin content. A single injection of selenite (20 micro mol/kg body wt) to 9-day rat pups results in 100% nuclear cataracts 72 hr later. In this experimental model, low molecular weight thiol and NADPH pools decrease prior to cataract formation. Again lens development needs to be understood since injection of pups 16 days or older will not form cataract. Potassium and sodium levels appear normal. These experimental cataracts are being evaluated in order to describe the biochemical events which lead to cataract formation and the relationship of these processes to nutritional status of the animal.